richbrummitt Posted July 17, 2012 Share Posted July 17, 2012 Here we go. I think I'm quite probably certifiable for having a crack at this and I'm already late to the party so I'm going for a bite of the apple by making just the engine for a Great Western steam railmotor. The engines took longer to return to service than the rest of the vehicle and so they were often swapped out so that the whole unit was not kept off the rails too long. The engine consists of just the front bogie upon which the gertical boiler and firebix was mounted. There was a railmotor service on the Thame branch so I can just about justify this, although it is certainly not a priority and so somewhat whimsical. My understanding is that these engines had the smallest Walschaert valve gear of any engine and being a Great Western modeller I haven't had to worry myself with anything so complex before. Using J. Lewis' book on the steam railmotors as a reference I have constructed a CAD model to try to work out whether I have the sizes of the various linkages right and if there's enough width t fit everything in without it hanging out from the sides of the body when that is finally built. With a bit of luck there will be an embedded animation below (if not this should take you directly to it http://www.flickr.co...itt/7590330294/ ) and with a little more good will someone will be able to tell me whether it looks right or not? I think I need to limit the travel of the valve spindle to fully constrain the mechanism. Fortunately there is an upcoming outing to Pendon and Didcot and just maybe I will be able to see the real thing running up close to find out first hand how it should look when in motion. <object type="application/x-shockwave-flash" width="400" height="250" data="http://www.flickr.com/apps/video/stewart.swf?v=109786" classid="clsid:D27CDB6E-AE6D-11cf-96B8-444553540000"> <param name="flashvars" value="intl_lang=en-us&photo_secret=b7ba6bcc74&photo_id=7590330294"></param> <param name="movie" value="http://www.flickr.com/apps/video/stewart.swf?v=109786"></param> <param name="bgcolor" value="#000000"></param> <param name="allowFullScreen" value="true"></param><embed type="application/x-shockwave-flash" src="http://www.flickr.com/apps/video/stewart.swf?v=109786" bgcolor="#000000" allowfullscreen="true" flashvars="intl_lang=en-us&photo_secret=b7ba6bcc74&photo_id=7590330294" height="250" width="400"></embed></object> TTFN, Richard. Link to post Share on other sites More sharing options...
Steve Sykes Posted July 19, 2012 Share Posted July 19, 2012 I suspect the prize for the smallest outside Walschaerts valve gear goes to the LSWR railmotors which were 0-2-2s with the cylinders and valve gear between the axles. The GW SRM is undoubtedly tiny, though. Geoff Jones built a model of the L&Y railmotors a good few years ago so may have some insights to offer. Good luck with the project. Link to post Share on other sites More sharing options...
buffalo Posted July 19, 2012 Share Posted July 19, 2012 You're a brave man, Richard! One day, I'll do a SRM, but that will be in 4mm where the valve gear will be small enough, but doing it in 2mm will be a real challenge. On your animation, the eccentric seems to have worked loose as it does not rotate fully with the wheel. There are some other animations on Wikipedia and which may help. Nick Link to post Share on other sites More sharing options...
RMweb Gold queensquare Posted July 19, 2012 RMweb Gold Share Posted July 19, 2012 I suspect the prize for the smallest outside Walschaerts valve gear goes to the LSWR railmotors which were 0-2-2s with the cylinders and valve gear between the axles. The GW SRM is undoubtedly tiny, though. Geoff Jones built a model of the L&Y railmotors a good few years ago so may have some insights to offer. Good luck with the project. Geoff found the valve gear so challenging that, for years, it was only fitted on one side. Don't know if the other side is now done. Jerry Link to post Share on other sites More sharing options...
-missy- Posted July 19, 2012 Share Posted July 19, 2012 I would be up for the challenge if you wanted anyone to test the bits out on...! M Link to post Share on other sites More sharing options...
richbrummitt Posted July 19, 2012 Author Share Posted July 19, 2012 You're a brave man, Richard! One day, I'll do a SRM, but that will be in 4mm where the valve gear will be small enough, but doing it in 2mm will be a real challenge. On your animation, the eccentric seems to have worked loose as it does not rotate fully with the wheel. There are some other animations on Wikipedia and which may help. Nick Thanks Nick, The YouTube link was particularly useful because it slowed right down. I can see that my animation is wrong but I don't know why. Maybe I have something drawn the wrong size/shape when tracing from the scanned drawing. More probably there is a constraint that I haven't considered. I'm going on the afternoon excursion to Didcot with anyone else from RMWeb after the Pendon visit next weekend so hopefully after digesting the Wikipedia page and seeing the real thing I'll be able to get it right. Link to post Share on other sites More sharing options...
RMweb Gold queensquare Posted July 19, 2012 RMweb Gold Share Posted July 19, 2012 I would be up for the challenge if you wanted anyone to test the bits out on...! M Me too, presumably you intend to do the rest of the railcar as well at some point. Which ones - the 70 footers hopefully! Jerry Link to post Share on other sites More sharing options...
richbrummitt Posted August 1, 2012 Author Share Posted August 1, 2012 The Didcot visit was most useful to this project and may also breed another if I can find an LED small enough. I have a lot of photos of bits of SRM. The cab is a very odd place to be, as you might imagine. With a bit of good fortune I should have some more drawings to be working from soon too. I found out what was wrong with the animation: the eccentric needs to have a fixed angle relative to the wheel and is therefore permanently fixed to the crank pin. Doh! When I made this constraint in the model it locked the whole thing solid but that is because I had made a pin joint of something that needed a very small amount of vertical movement in addition to the rotation. I feel much happier about this now and should be able to move things forward soon. Link to post Share on other sites More sharing options...
richbrummitt Posted August 10, 2012 Author Share Posted August 10, 2012 With thanks to some very helpful individuals I have more drawings. :-D Quite a lot of drawings in fact. My animated model has been corrected and looks much better! The next step is to check and validate the lengths and assembly orders for the motion components to achieve the compromise of fitting everything in the space and it looking something like the real thing. That will take some time with very little to show for it. After that there is the decision whether to draw and etch or mark out and cut. The latter might allow the links to be more true to form where some of the links have forked joints. Fluted rods are a pain to make though when compared with etching. It's not such a straightforward decision that one. Link to post Share on other sites More sharing options...
richbrummitt Posted August 29, 2012 Author Share Posted August 29, 2012 This will still happen, and soon, however it will not be in time for the competition deadline. I've since picked up and run with another project, a GWR point disc, details of which can be found in another topic here. Link to post Share on other sites More sharing options...
Castle Posted August 31, 2012 Share Posted August 31, 2012 Hi Rich, Make sure you open a topic in the Kit and Scratchbuilding Forum on this one - I will continue to enjoy this thread and report progress back to Graham and the No. 93 team on progress! Perhaps an application to the Moderators for a move is in order here? All the best, Castle Link to post Share on other sites More sharing options...
richbrummitt Posted August 31, 2012 Author Share Posted August 31, 2012 I'll stick it somewhere on here, for sure. I need to get into the drawings properly and I know that the deadline is out of the question, especially with a week out for a holiday too. Most of my output is blogged, but I have enjoyed the input from the thread on the point disc so I could be tempted to try it again with another project. Link to post Share on other sites More sharing options...
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